1. Field of the Invention
The present invention relates to a scanning element for a position measuring instrument.
2. Discussion of Related Art
In addition to position measuring instruments in which a periodic scale is optically scanned to obtain position-dependent information, measuring systems are known that are based on alternative scanning principles. Such position measuring instruments prove to be less vulnerable, especially under certain environmental conditions, than the aforementioned optical measuring systems. Such environmental conditions exist for instance in applications in which the rotary motion of the shaft of a drive mechanism is to be detected. A position measuring instrument which can be used even under relatively rough environmental conditions is described for instance in European patent disclosure EP 0 289 033 B1. In it, a scale track of alternatingly arranged electrically conductive and nonconductive regions is scanned inductively. The corresponding scanning element to that end has one or more exciting coils, which, in the region of the scanned scale track, generate a homogeneous electromagnetic field. On the scanner side, sensor windings are also provided, which are also disposed in the homogeneous field of the exciting coils and serve to detect the electromagnetic fields induced in the conductive regions of the scale track, so that an output signal modulated as a function of displacement results. In this way, the relative motion between the scale track and the scanning element can be detected. In terms of the functional principle of such a position measuring instrument, reference may also be made to European Patent Disclosure EP 0 182 085.
A similarly designed inductive position measuring instrument is also known from German Patent Disclosure DE 195 04 307. There it is proposed, among other things, not merely to scan a single scale track but instead to provide further tracks that can be read out in the manner described. Details of the concrete embodiment of a measuring arrangement with a plurality of scanned scale tracks and possibilities for generating the exciting fields, however, are not disclosed in this reference.
Another inductive position measuring instrument that operates by the principles mentioned above is also known from European Patent Disclosure EP 0 743 508 A2. Once again, however, this reference provides no indication of how in the case of a plurality of scanned scale tracks, for instance, the scanning element should be concretely designed. In particular, there is no indication how for the various scanning tracks the generation of the most homogeneous possible exciting fields might be accomplished.
An object of the present invention is therefore to embody a scanning element of this generic type for an inductive position measuring instrument in such a way that even if a plurality of scanning tracks are provided, reliable functioning is assured. In particular, even for a plurality of scanning tracks, the generation of homogeneous exciting fields in the region of the various scanning tracks should be assured.